This invention relates to a pressure sensitive apparatus. More particularly, it relates to a pressure sensitive apparatus of improved novel structure conforming with the semiconductor strain gauge type which exploits the piezoresistance effect and in which a resistance is formed in a semiconductor single crystal by diffusion.
Heretofore, there has been widely known a pressure sensitive apparatus of the semiconductor strain gauge type wherein a p-type resistance region is selectively diffused in an n-type silicon semiconductor single crystal to form a pressure sensitive element, a strain develops upon application of a pressure to the element, and a resistance change of the p-type resistor owing to the piezoresistance effect is measured so as to detect the value of the pressure.
In U.S. Pat. No. 4,019,388, for example, there is disclosed a pressure sensitive apparatus which has a silicon chip indirectly bonded to a stainless steel housing of an electronic pressure transmitter through an intermediate nickel-iron alloy. This indirect bonding prevents thermal cracking of the silicon chip due to the difference in thermal expansion between the stainless steel housing and the silicon chip. The holder assembly includes a borosilicate glass tube having the silicon chip bonded thereto which tube is soldered to the nickel-iron alloy holder by a eutectic alloy solder. In assemblage, the nickel-iron holder is first brazed to the stainless steel housing at a first temperature greater than the maximum non-destructive temperature of either the chip or the glass tube, and the glass tube is then soldered to the nickel-iron holder at a lower temperature which will not destroy the chip or the tube holder. However, the above-mentioned soldering is very troublesome, for example because the joined surface of the nickel-iron holder and the glass tube is coated with a thin chromium layer and a thin gold layer by evaporation or the like prior to the soldering.
Other relevant prior arts are as follows:
(1) U.S. Pat. No. 3,918,019, "MINIATURE ABSOLUTE PRESSURE TRANSDUCER ASSEMBLY AND METHOD";
This shows a silicon diaphragm assembly which is bonded on a glass substrate in accordance with the anodic bonding technique.
(2) U.S. Pat. No. 3,397,278, "ANODIC BONDING";
This relates to the anodic bonding technique.